From: Patrick Jankowiak (recycler@swbell.net)
Date: Wed Mar 08 2006 - 18:06:52 PST
No 3-terminals, you need an inductor and a diode to go a-switching, but it
is very simple to do. Another post is correct regarding simple linear
regulators: all they do is 'eat' half (in this case) of the voltage and
waste it as heat.
About simple switchers, These datasheets show not only specs, but
demonstration circuits, with various outputs.
here's a 10A switcher IC the L4970A
http://www.st.com/stonline/products/literature/ds/1361/l4970a.pdf
and the same for 7 amps:
http://www.st.com/stonline/products/literature/ds/1365/l4977a.pdf
and for 5 amps:
http://www.st.com/stonline/products/literature/ds/1364/l4975a.pdf
and 2.5 amps:
http://www.st.com/stonline/products/literature/ds/1356/l4960.pdf
It's a shameless plug for my company's products of course, but any of these
are good for 24-to-12 converters, come in hobbyist-friendly packages, and
you can set the output voltage exactly to 12.6, 13.2, or whatever you want,
with a simple resistor value. The larger ones also have soft start.
If you want to go it alone with discrete parts, see figure 3 on this page,
which I used to convert 10-15VDC to a regulated 6.3V for operating vacuum
tube filaments in a car. It is not optimized, but it works well. The
voltages can all be changed and you will have to attend to some re-design.
http://www.montagar.com/~patj/tubeart.htm (this makes the IC's solution
look pretty good actually)
Patrick
Alex wrote:
> OK... I'm a little of a microgeek. How about something along this line per
> bulb for the mil 24 volt headlights? Any simple 3 terminal device that will
> handle the 6 amps or so? I hate buying 24volt headlights. :(
> Alex
>
> -----Original Message-----
> From: Military Vehicles Mailing List [mailto:mil-veh@mil-veh.org] On Behalf
> Of Patrick Jankowiak
> Sent: Friday, March 03, 2006 11:21 PM
> To: Military Vehicles Mailing List
> Subject: Re: [MV] TRAILERS --
>
> One thing could be done, to use a small 24-to-12 switching power supply
> (buck converter) for each lamp to be lit on the trailer. 24V/1A in, 12V/2A
> out.. less any inefficiencies.
>
> truck socket sees proper currents, trailer lamps see proper voltages.
> (unless you have a fat wallet, you should make your own switchers.)
>
> This could also be done cheeply with any solid state circuit that would
> turn the power on and off maybe 100 times a second with a 50% duty cycle.
> Would not need a full blown regulated switcher. (visions of a 555 timer and
> a BDW94CFP (12A PNP Darlington in an isolated TO-220 case))
>
> but that's for geeks, making your own electronics.
>
> The easiest and cheapest thing by far (other than changing lamps) is to add
> a second set of lamp fixtures with 24V lamps to include the proper
> connector for your truck's trailer socket. Besides, due to the oddities of
> various brake light wiring schemes among civvy vehicles, you may not want
> to mix and match the wiring.
>
> PJ
>
> Arthur Bloom wrote:
>
>
>>----- Original Message -----
>>From: "Ryan Gill" <rmgill@mindspring.com>
>>To: "Military Vehicles Mailing List" <mil-veh@mil-veh.org>
>>Sent: Friday, March 03, 2006 2:46 PM
>>Subject: Re: [MV] TRAILERS --
>>
>>
>>At 9:58 AM -0700 3/3/06, SGM PANTANO wrote:
>>
>>
>>>Hey...wake up.. There is no such thing as a 24 volt or a 12 volt trailer..
>>>The light receptacles in the Military tail lights could care less what
>
> bulb
>
>>>is in there..
>>
>>
>>But the wiring could. 24 volt wires could be
>>sized smaller, try to run the same wattage bulb
>>at 12 volts and you could fry your wires. Check
>>the wire harness first!
>>
>>
>>
>>Twelve gauge copper wire has an ampacity of 41 in open air (single
>
> insulated
>
>>conductor) and an ampacity of 23 in a harness. For 14 gauge wire, the
>>ratings are 32 amps and 17 amps, respectively. It would take a lot of
>
> lamps
>
>>to reach those limits. In addition, there are fuses which are designed to
>>fry before the wires do.
>>
>>Arthur P. Bloom
>>
>>
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>>
>
>
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>
>
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